Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic technique or an electrostatic recording technique.
Description of the Related Art
Conventionally, in an intermediate-transfer image forming apparatus, as a method for removing a residual toner from an intermediate transferring member and collecting the residual toner, there is a method of charging the residual toner with the reverse polarity of a regular charge polarity, transferring the residual toner to a photosensitive member by a primary transfer unit and collecting the residual toner by a cleaning device for the photosensitive member.
Here, a cleaning blade (hereinafter, merely referred to as a “blade” also) is used as the cleaning device for the photosensitive member. The cleaning performance of the cleaning blade is greatly influenced by the condition of a blocking layer that is formed at a tip of the blade by an external additive of a toner (Japanese Patent Application Laid-Open No. 2006-184689). When the blocking layer is not sufficiently formed, the friction on the abutting portion between the blade and the photosensitive member produces a crack or flaw of the tip of the blade, or a tear or stick-slip (chatter) of the blade, and this sometimes causes the toner and the external additive to slip through the blade.
However, the construction of transferring the residual toner to the photosensitive member and removing the residual toner by the blade has the following problem. For example, when the regular charge polarity of the toner is the negative polarity, the residual toner charged with the positive polarity on the intermediate transferring member is transferred to the photosensitive member, at the same time that the toner with the negative polarity is primarily transferred to the intermediate transferring member, and then the residual toner is removed from the photosensitive member by the blade. On this occasion, in an image forming unit right after the charge with the positive polarity (on the most upstream side in the moving direction of the intermediate transferring member), a greater amount of the residual toner is transferred to the photosensitive member, compared to the other image forming units.
It has been found that the toner and the external additive of the toner easily slip through the blade in the image forming unit in which a large amount of the toner with the positive polarity is fed to the blade in this way. In some cases, the slipped toner and external additive adhere to a charging member that charges the photosensitive member, obstruct a uniform charge of the surface of the photosensitive member, and cause a density unevenness of the image.